EXT:fluid uses @api and @internal phpDoc annotations. Going with a cleaner
approach with marking code as just @internal, and everything not annotated
as @internal is public, is the way to go, also the way PSR-5 is heading.

For EXT:fluid: Every PHP class that had nothing marked, is now @internal,
everything that was @api is now implicitly part of TYPO3 Core API.

Other areas will follow so the API for TYPO3 v9 LTS is clearer than ever.